The best 4.0 L Cylinder head made? - JeepForum.com
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post #1 of 18 Old 12-22-2012, 07:13 PM Thread Starter
94beachxj
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The best 4.0 L Cylinder head made?

After some research I have concluded the 1991-95......#7120 casting was the best for these Cherokee engines.
My ATK replacement engine was from a AMC 92-95 block.
I guess that puts me in the better of the mix?
What I have found on the other side is the 1999-04......#0331 casting was the worst casting, hence the over heating and cracked heads.
The # 2 cylinder area had weakness to the best of my knowledge.
Whats your thoughts on this?

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post #2 of 18 Old 12-22-2012, 08:17 PM
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Originally Posted by 94beachxj View Post
After some research I have concluded the 1991-95......#7120 casting was the best for these Cherokee engines.
My ATK replacement engine was from a AMC 92-95 block.
I guess that puts me in the better of the mix?
What I have found on the other side is the 1999-04......#0331 casting was the worst casting, hence the over heating and cracked heads.
The # 2 cylinder area had weakness to the best of my knowledge.
Whats your thoughts on this?
#7120 is generally considered the best. The #0331 from 2000-01 is generally considered the worst (very few 99s have the #0331 head, only those from the very end of the model year with coil packs have it). From 02+ the #0331 head problem was fixed for the most part, the corrected heads have TUPY stamped in the center.

The weakness in #0331 heads is generally between #3 and #4 cylinders. That being said #0331 is not absolutely terrible, they usually only crack if overheated. If you bought a 2000-01 new, maintained the cooling system properly, and never overheated it the odds of a cracked head are very slim, however if you buy one used you don't know the history and whether or not it has ever been overheated in the past, so there is always a risk of a cracked head on a used 2000-01.
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post #3 of 18 Old 12-22-2012, 08:34 PM
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I agree with dmill89. The 0630 and the 7120 heads are considered the best performing and would be fine for any Jeep 4.0L. Actual cracked 0331 heads are very many fewer than the number of threads on various forums about them cracking. IMO nearly all cracked 0331 heads are the results of abuse through neglected cooling system maintenance.

A simple low cost preemptive 0331 plan is to locate a good used TUPY 0331 cylinder head with the upgraded and more crack resistant casting. 2002+ TJ and WJ 4.0L at the junkyard are suitable donors. Have the head inspected, and install it before any potential cylinder head issues come up. At 139,000+ miles, my 2000 0331 head is still good, but I have a TUPY 0331 head getting ready for a swap.

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post #4 of 18 Old 12-23-2012, 06:06 AM Thread Starter
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Originally Posted by CJ7-Tim View Post
I agree with dmill89. The 0630 and the 7120 heads are considered the best performing and would be fine for any Jeep 4.0L. Actual cracked 0331 heads are very many fewer than the number of threads on various forums about them cracking. IMO nearly all cracked 0331 heads are the results of abuse through neglected cooling system maintenance.
So true!
I use the "green stuff" and keep it fresh ! I made a thread a while back on how I rotate the new coolant in the system a little at a time. I will never need to flush a coolant system again using this method.
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post #5 of 18 Old 12-23-2012, 08:41 AM
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Originally Posted by dmill89 View Post
The #0331 from 2000-01 is generally considered the worst
Wrong. The 87-90 head, whatever number it is (686?), is the worst.

Furthermore, a head (or any other part for that matter) is only as good as the other parts around it. These parts all work in concert with each other and just swapping a head won't do much for you if you're not using a complimentary cam/intake/exhaust. The same can be said to all the people who think slapping a 99+ intake on an older engine will actually do something without a head/cam/exhaust to support it.

If you're building a custom 4.0 (or stroker) with all sorts of fancy parts, porting, polishing, the 7120 is the head to work with, but if you're just in need of a new head for your workhorse, it won't really make much of a difference.

0331 cracking issues? Way overexposed. The problem is real, but it is seriously exaggerated by the fact that people will log onto the web to say when theirs is cracked, but will never make posts advertising when there's HASN'T. There are a ton of 0331 heads out there that are just fine. Real problem, so always keep an eye on it, but just because you may have a 0331 doesn't mean you're fated for failure like people on the internet would have you believe.
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post #6 of 18 Old 11-05-2013, 06:48 AM Thread Starter
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Wrong. The 87-90 head, whatever number it is (686?), is the worst.

0331 cracking issues? Way overexposed. The problem is real, but it is seriously exaggerated by the fact that people will log onto the web to say when theirs is cracked, but will never make posts advertising when there's HASN'T. There are a ton of 0331 heads out there that are just fine. Real problem, so always keep an eye on it, but just because you may have a 0331 doesn't mean you're fated for failure like people on the internet would have you believe.
I agree to a point. But if you change the coolant once a year, the green stuff will be your friend! The 4.0 runs hot with lots of pressure! One way to save that hot block.................be cool
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post #7 of 18 Old 02-18-2021, 08:04 PM
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I agree to a point. But if you change the coolant once a year, the green stuff will be your friend! The 4.0 runs hot with lots of pressure! One way to save that hot block.................be cool
Quick question, what's "the green stuff"? Any specific brands you're referencing or just the 50/50 prediluted mix?
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post #8 of 18 Old 02-19-2021, 04:38 AM
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Quick question, what's "the green stuff"?
Plain old everyday ethylene glycol green coolant.

Ethylene Glycol coolant should be changed every 30,000 miles or every two years to prevent corrosion, rust, and overheating.
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post #9 of 18 Old 02-21-2021, 01:09 PM
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We have two vehicles with the 0331 heads. Both were used/abused by women. The '01 with 100k cracked and required a total engine rebuild. The '00 has 180k and is still chugging along with no issues. Since both were neglected equally I have to think it is a 50-50 chance if it lasts or not.

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post #10 of 18 Old 02-22-2021, 07:39 AM
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Quote:
Originally Posted by AndyIA01 View Post
Quick question, what's "the green stuff"?
Plain old everyday ethylene glycol green coolant.

Ethylene Glycol coolant should be changed every 30,000 miles or every two years to prevent corrosion, rust, and overheating.
Thank you! Trying to find that in my area right now. I need to drain and replace the coolant before it starts warming up this spring.
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post #11 of 18 Old 02-23-2021, 10:24 AM
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andy, you should be able to get it at Walmart, your local supermarket actually might have it on the section with the car and lights bulb stuff, and of course, the local autoparts place will have it

the xj is the only jeep left in the driveway
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post #12 of 18 Old 05-09-2021, 01:38 AM
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Quote:
Originally Posted by mschi772 View Post
Quote:
Originally Posted by dmill89 View Post
The #0331 from 2000-01 is generally considered the worst
Wrong. The 87-90 head, whatever number it is (686?), is the worst.

Furthermore, a head (or any other part for that matter) is only as good as the other parts around it. These parts all work in concert with each other and just swapping a head won't do much for you if you're not using a complimentary cam/intake/exhaust. The same can be said to all the people who think slapping a 99+ intake on an older engine will actually do something without a head/cam/exhaust to support it.

If you're building a custom 4.0 (or stroker) with all sorts of fancy parts, porting, polishing, the 7120 is the head to work with, but if you're just in need of a new head for your workhorse, it won't really make much of a difference.

0331 cracking issues? Way overexposed. The problem is real, but it is seriously exaggerated by the fact that people will log onto the web to say when theirs is cracked, but will never make posts advertising when there's HASN'T. There are a ton of 0331 heads out there that are just fine. Real problem, so always keep an eye on it, but just because you may have a 0331 doesn't mean you're fated for failure like people on the internet would have you believe.


I know this is an olldddd thread.... but.... Curious, why is the 2686 head the worst?
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post #13 of 18 Old 05-09-2021, 05:24 AM
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Quote:
Originally Posted by mschi772 View Post
Wrong. The 87-90 head, whatever number it is (686?), is the worst.

Furthermore, a head (or any other part for that matter) is only as good as the other parts around it. These parts all work in concert with each other and just swapping a head won't do much for you if you're not using a complimentary cam/intake/exhaust.

if you're just in need of a new head for your workhorse, it won't really make much of a difference.
Well, sort of true. The 7120 and late heads have a different exhaust bolt pattern (THAN THE OLDER PRE- 87 HEADS), so you HAVE TO CHANGE the exhaust. You DO NOT HAVE TO CHANGE the intake though. If you do drop a 7120 on an old motor you STILL GET BENEFITS, although not quite as much when you do further upgrades.

Last edited by gutthans; 05-09-2021 at 07:19 AM. Reason: clarity
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post #14 of 18 Old 05-09-2021, 06:21 AM
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All Jeep in-line 6 cylinder heads have the same bolt hole pattern. The 2000-01 # 0331 head has slightly different exhaust port locations than the 1999 and older heads, and the 1999 and older stock exhaust manifold do not fit properly on the 0331 head without an adapter plate.


The early '87-'90 non-HO heads have low intake ports that flow rather poorly. The later HO heads have higher intake ports that flow more air by allowing a straighter shot into the cylinders. The '91-'95 HO heads with casting # 7120 have the highest intake and exhaust port airflows, especially at lower valve lifts where it is most important, and are the best for performance. The '96-'99 0630 heads are almost identical except that they don't have a port for the coolant temp. gauge sending unit. The '00 and later HO heads with casting # 0331 have smaller exhaust ports to produce a faster warm-up of the catalytic converter and improve emissions, but performance also suffers because the ports don't flow as well as those of the 7120 and 0630 castings.

4.0 L Cylinder head

The stock 4.0 L cylinder head is cast iron and weighs 60lb. The valve head diameter is 1.91" intake/1.50" exhaust.

Casting numbers are :

Year............Casting #
1987-90......2686
1991-95......7120
1996-99......0630
2000-01......0331

Cylinder head flow figures (cfm) at 28in H2O pressure drop are:

Non-HO head #2686
Valve lift (in)..... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 122.0 168.0 186.0 189.0 192.0
Exhaust flow....88.0 114.0 130.0 134.0 138.0

HO head #7120 & #0630
Valve lift (in)... 0.1 ... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 66.0 128.0 179.0 206.0 209.0 209.0
Exhaust flow. 55.0 100.0 120.0 136.0 141.0 141.2

HO head #0331
Valve lift (in)..... 0.1 ... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow..... 59.4 122.6 171.1 201.1 214.3 218.4
Exhaust flow...47.1 93.4 123.3 140.9 147.0 149.7

“We the people are the rightful masters of both Congress and the Courts,
not to overthrow the Constitution but to overthrow the men who would pervert the Constitution” Abraham Lincoln, 1859.
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post #15 of 18 Old 05-09-2021, 07:15 AM
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Quote:
Originally Posted by CJ7-Tim View Post
All Jeep in-line 6 cylinder heads have the same bolt hole pattern.
I believe your statement is either incomplete or simply incorrect. Please view the rebuilt heads at: https://www.jegs.com/p/ATK-Engines/A...63244/10002/-1

and tell me the center bolt configuration at intake runners 3 & 4 is the same for 258 and 4.0 inline 6 heads??? Unless I'm blind (which does happen from time to time) the pattern changes somewhere around 1987.

Perhaps I wasn't clear when I mentioned 7120's and later heads...I meant that they were different from earlier 258 heads.
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